1. Field of the Invention
In one aspect, the invention relates to an oven having accurate temperature control including a baking cavity with independently-controlled bake and broil heating elements via separate temperature sensors located adjacent each of the corresponding heating elements. In another aspect, the invention relates to a method for independently controlling the bake and broil heating elements in the baking cavity of the oven during a bake cycle of the oven.
2. Description of the Related Art
Electric- and gas-based cooking ovens are old and well-known in the prior art. With reference to FIG. 1, these types of ovens 10 typically comprise an open-face housing defining a baking cavity 12, with the open face enclosed by a hinged door 14. The open face housing is formed by opposing top and bottom walls, opposing end walls, and a rear wall. A broil heating element 16 is mounted adjacent the upper wall of the baking cavity 12 and a bake heating element 18 mounted adjacent the lower wall of the baking cavity. The side walls 20, 22 are provided with rack supports 24 extending generally in horizontal fashion depth-wise into the baking cavity 12 along the side walls 20, 22 for supporting a baking rack 26 thereon.
In control methods for prior art ovens 10, a single temperature sensor 28 is typically located a predetermined distance from each of the broil and bake heating elements 16, 18, respectively, such as along a medial horizontal plane of the baking cavity 12 as shown in FIG. 1. This single temperature sensor 28 was typically used in bake and broil modes of prior art ovens 10 to control the activation and deactivation of the broil and bake heating elements 16, 18.
The use of a single temperature sensor 28 in prior art ovens 10, especially such a sensor 28 spaced a great distance from the associated broil and bake heating elements 16, 18, has not shown to be an effective method by which to produce a constant and effective heating gradient across the vertical height of the baking cavity 12 since heat rises and because the heat differential across the vertical height of the baking cavity can be substantially affected by various types of food products placed on the cooking rack 28 (e.g., a frozen poultry product versus a room temperature mixture) and the shape and size of the pan holding the food product.
For example, the pan interferes with the vertical flow path of the heat air rising from the bake element. Typically, the larger the pan, the greater the interference. The interference results in the heated air building up along the bottom of the pan and flowing around the sides of the pan, which prevents an even distribution across the top of the pan, resulting in a region of lower temperature air above the pan and very heated air below the pan. The food product can exacerbate the low temperature region if the food product is at substantially lower temperature than the surrounding air, effectively functioning as a cooling point source. The end result is an undesirable temperature gradient on opposite sides of the pan.
It has been found that the location of a single temperature sensor 28 located at upper end of the baking cavity 12 is ineffective in providing input to a controller for activating and deactivating the broil and bake heating elements 16 and 18 in a manner capable of reducing or eliminating the temperature gradient across the pan.
There have been prior art attempts to install multiple temperature sensors 28 in the baking cavity 12 of an oven 10, however, these prior art attempts have been to solve problems unrelated to the even heating along the height of the oven cavity.
For example, U.S. Pat. No. 5,723,846 to Koether, et al., issued Mar. 3, 1998, discloses the use of a pair of temperature sensors located adjacent heating elements both located on an upper wall of a baking cavity in a convection oven used for error detection purposes in sensing error conditions in the convection oven.
U.S. Pat. No. 5,791,890 to Maughan, issued Aug. 11, 1998, discloses a temperature sensor located adjacent each bake and broil heating element in a gas oven used for the purpose of detecting a positive proof of ignition in each of the gas-based heating elements.
U.S. Pat. No. 5,332,886 to Schilling et al., issued Jul. 26, 1994, discloses an electronic regulator for an electric oven having a controller provided with a fixed program to process data from a real temperature sensor and separate temperature sensors for producing error correction values on the ambient temperature in the baking cavity for converting the dependence between the temperature values of the real temperature sensor and the measuring temperature device into additional process data.
None of the dual sensor applications address the problem of accurately controlling the temperature of the oven baking cavity during a bake cycle of the oven to obtain an even heat distribution along the height of the oven.
The invention relates to a method for accurately controlling the ambient temperature in an enclosed baking cavity of an oven that is preheated with respect to a user-set temperature set point. The baking cavity of the oven comprises a broil heating element mounted to an upper portion of the baking cavity and a bake heating element mounted to a lower portion of the baking cavity, thereby defining a baking region therebetween. A broil temperature sensor is mounted within the baking cavity adjacent to the broil heating element. Similarly, a bake temperature sensor is mounted within the baking cavity adjacent to the bake heating element.
One method of controlling the oven comprises the following steps: providing a controller capable of actuating the broil and bake heating element in response to broil and bake temperature sensors; determining a target temperature set point for the oven cavity based on the user-set temperature set point; sensing the temperature of the baking region adjacent at least one of the bake and broil heat elements; comparing the sensed temperature with the target temperature set point; and, selectively actuating the broil and bake heating elements in response to the sensed temperature to maintain a vertical temperature distribution in the oven cavity that is substantially equal to the target temperature set point.
The steps in determining a target temperature set point can comprise calculating the heating element set point comprising one of a broil set point and a bake set point derived from the target temperature set point. The calculation of the bake and broil element set points preferably comprises selecting the one of the bake and broil set points from a data table containing a list of target temperature set points and a corresponding list of at least one of the bake and broil set points. The bake and broil set points preferably comprise a range of temperature values delimited by a low temperature limit and a high temperature limit.
Alternatively, the calculation of the broil and bake set points can comprise selecting a temperature differential value corresponding to the target temperature set point and summing the temperature differential value with the selected at least one of the bake and broil set points to calculate the other of the at least one of the bake and broil set points. The temperature differential value can be either negative or positive.
The step of sensing the temperature preferably comprises reading a sensor temperature signal comprising one of a bake temperature signal and a broil temperature signal read from the corresponding bake temperature sensor and broil temperature sensor.
The selective actuation of the broil and bake heating elements preferably comprises alternately activating the bake and broil heating elements. The alternate activation typically includes deactivating the heating element corresponding to the sensed temperature if the sensed temperature exceeds the corresponding heating element set point, activating the heating element corresponding to the sensed temperature if the sensed temperature is less than the corresponding heating element set point, and deactivating the heating element other than the heating element corresponding to the sensed temperature if the sensed temperature is less than the heating element set point. Preferably, only one heating element is activated at a time. Also, the activation of the bake and broil heating elements is preferably continued for a predetermined duty cycle as long as the other bake and broil element is deactivated.
The method can further comprise the step of detecting whether the oven is gas-based or electric based. If the oven is gas based, the method can include determining whether a purge time limit for the broil heating element has been satisfied.
The method can also comprise compensating the heating element set point based upon an initial heating condition of the baking cavity. The heating element set point is preferably increased in the compensation step. The compensation step can further comprise adjusting the heating element set point according to a predefined function, which is preferably a decreasing linear function.
In another aspect, the invention relates to an oven incorporating accurate ambient temperature control. The oven comprises a housing defining an enclosed baking cavity. At least one oven rack for supporting a pan is disposed within the cavity and conceptually divides the cavity into an upper heating region above the rack and a lower heating region below the rack. A broil heating element is mounted in the upper heating region of the baking cavity. Similarly, a bake heating element is mounted in the lower heating region of the baking cavity. A broil temperature sensor is mounted within the upper heating region adjacent to the broil heating element. Similarly, a bake temperature sensor is mounted within the upper heating region adjacent to the bake heating element. A controller is operably interconnected to a power source and to the broil heating element, bake heating element, the broil temperature sensor and the bake temperature sensor for selectively actuating the broil heating element and the bake heating element in response to the sensed temperatures of the upper and lower heating regions to maintain the temperature of the upper and lower heating regions substantially equal to a target temperature set point.
The controller preferably calculates the heating element set point comprising one of the broil set point and a bake set point derived from the target temperature set point. A sensor temperature signal comprising one of a bake temperature signal and a broil temperature signal is read from the corresponding heating element sensor comprising one of the bake temperature sensor and broil temperature sensor. The controller preferably compares the sensor temperature signal to the heating element set point. The controller deactivates the corresponding heating element if the sensor temperature signal exceeds the heating element set point. The controller also activates the corresponding heating element if the sensor temperature signal is less than the heating element set point. The controller can deactivate the heating element other than the corresponding heating element if the sensor temperature signal is less than the heating element set point.
Preferably, the controller includes a database comprising multiple target temperature set points and corresponding broil set points and bake set points, whereby the bake and broil set points can be selected from the table according to the target temperature set point. Preferably, the broil set point and the bake set point each comprise a range of temperature values delimited by a low temperature limit and a high temperature limit.
The controller deactivates one of the bake and broil heating elements if one of the bake and broil elements is activated and if the corresponding bake or broil temperature signal exceeds the corresponding bake or broil set point by a predetermined amount. The controller activates one of the bake and broil heating elements for a predetermined duty cycle as long as the other of the bake and broil heating elements is deactivated.
The controller can compensate the heating element set point based upon an initial heating condition of the baking cavity. The compensation increases the heating element set point. Preferably, the compensation adjusts the heating element set point according to a predefined function, which is preferably a decreasing linear function.
In yet another aspect, the invention relates to a method for maintaining an even temperature distribution in a baking cavity of an oven relative to a user-defined temperature set point. The baking cavity of the oven comprises a rack for supporting a pan, with the rack functionally dividing the cavity into an upper heating region above the rack and a lower heating region below the rack. A broil heating element is provided in the upper heating region along with a corresponding broil temperature sensor. A bake heating element is provided in the lower heating region along with a corresponding bake temperature sensor. The method comprises the steps of: providing a controller capable of actuating the broil and bake heating elements in response to the broil and bake temperature sensors; determining a target temperature set point for the oven cavity based on the user-selected temperature set point; sensing the temperature of the upper and lower heating region; comparing the sensed temperatures with the target temperature set point; and selectively actuating the broil and bake heating elements in response to the sensed temperatures to maintain the temperature of the upper and lower heating regions substantially equal to the target temperature set point.